1. Sift flour, baking powder, salt and baking soda onto wax paper.
2. Beat butter or margarine with brown and granulated sugars until fluffy in a large bowl with electric mixer at high speed; beat in eggs and vanilla. Stir in flour mixture, a third at a time; blend to make soft dough.
3. Divide dough evenly into 3 parts. Flavor, shape and decorate each, following individual directions.
4. Bake in moderate oven (350°) 10 minutes, or until golden. Remove from cookie sheets with spatula to wire racks; cool completely.